It is desirable in underground mining of ore to monitor the flow of ore through the mine. Effectively monitoring the flow of ore can assist in the calibration and validation of predictive ore flow models. Knowing the origin of the ore passing through the mine's haulage network also enables the grade of ore being delivered to the mill to be anticipated. This can help the mine operate more efficiently and improve recovery.
A known method of monitoring the flow of ore in cave mining (including block caving and sub-level caving) is to install mechanical markers in the ore body and retrieve the mechanical markers as they are transported through an ore pass or haulage tunnel, for instance by using electro-magnets near the crusher. The mechanical markers are installed in holes strategically drilled in the ore body and their positions recorded. One example of mechanical markers used in ore flow tracking is sections of steel pipe having individual welded identifiers. Markers may take from hours to years to pass through a mine and in the case of sub level caving markers may take up to 5 years before being excavated and in the case of block caving up to 10 years. Mechanical markers are not easily recoverable as recovery relies on the marker detection awareness of personnel and markers may be difficult to identify within the ore being transported. A lack of diligence on the part of miners can result in poor recovery rates. Also, steel markers give a poor data resolution, because they are recovered relatively late in the ore process, and are usually recovered daily (rather than in real time).
An alternative method which has been proposed for sub-level caving is to seed the muck piles resulting from blasting with radio frequency identification (RFID) markers. The RFID markers are then tracked by RFID readers placed along the haulage network. In order for this method to operate effectively a geologist must be at each blast site to seed the muck pile after blasting. As will be appreciated, the resolution of ore origin is not as fine when seeding the muck piles after blasting as when installing mechanical markers in the ore before blasting. It is also inconvenient, labour intensive and a health and safety risk to have a geologist seed the muck pile after every blast. The RFID markers can not be installed in the ore body before blasting as presently available RFIDs are not able to consistently withstand the shock of blasts in sub-level caving. Other challenges faced by the RFID markers are the length of time they have to remain active before detection and having to transmit their ID signal to the RFID readers through ore.
To operate in the harsh environment of an underground mine the RFID markers must meet rigorous mechanical and electronic standards. To date, the known mine markers fail on both counts. In particular, the known marker housings do not provide the necessary ruggedness to provide long life and reliability.